Modern spacecraft use control moment gyros (CMGs) and/or rotating inertia wheels to provide attitude control. Inertia wheels combined with motor generators (M/Gs) are commonly referred to as reaction wheels (RWs). Multiple RWs may be combined to form a reaction wheel array or assembly (RWA). In general multiple CMGs or RWs oriented in different directions are used. Angular momentum stored in rotating inertia wheels within the CMGs or RWAs is converted to torque which is exchanged with the spacecraft to change its attitude in space. Torque is the time derivative of angular momentum. Reaction wheels have also been proposed for energy storage in spacecraft, a separate function. Sometimes, RWAs have been used in a combined function wherein they provide torque for attitude control and also exchange electrical energy with the spacecraft power bus.
An important consideration in spacecraft design, operation and capability is the power drain placed on the spacecraft power supply and the load placed on the spacecraft energy dissipation system (energy dump) to accelerate and decelerate the rotors during operation of the CMGs and RWAs. In general, CMGs use constant speed motors, require relatively low peak power and deliver higher torque but are significantly more complex and relatively expensive. RWAs are less expensive and sometimes easier to implement but achieving high torque over the desired momentum range usually requires high peak power input and/or dissipation that is often beyond the capability of many spacecraft. The power problems associated with conventional RWAs are more severe in smaller spacecraft where cost, power, weight, and reaction time are critical factors. Accordingly there continues to be a need for momentum control and torque transfer devices that are well suited for smaller spacecraft, that is, that combine relatively low cost and high torque capability with low peak power drain and energy dissipation.
Accordingly, it is desirable to provide improved momentum control apparatus and methods that are suited for use in smaller spacecraft or spacecraft requiring high torque at comparatively low cost with low peak power drain and dissipation. In addition, it is desirable that the apparatus and method be simple, rugged and reliable. It is further desirable to use RWA type momentum control devices in a way that can provide high torque without creating large peak loads on the spacecraft power and dissipation system. Still further, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.